In a great number of consumer product markets, particularly those which are low-margin and/or price-driven, an ongoing need exists for various manners of reducing product costs. For example, just-in-time manufacturing techniques, which reduce costs through minimizing inventory, have grown in prominence. In addition, improved packaging techniques and materials are constantly being developed to minimize the packaging component of product costs.
Just-in-time manufacturing can place significant demands on product manufacturing and packaging equipment due to the quick turnaround that is often required to timely fill customer orders. As a result, there is an ongoing need for a manner of increasing the speed of product manufacturing and packaging equipment so that inventory costs can be reduced without adversely impacting a manufacturer's ability to fill customer orders in a timely fashion.
For example, for bottled beverages such as soft drinks, beer, juice, liquor, etc., significant efforts have been expended in attempting to lower the costs associated with applying product labels to beverage containers such as glass bottles, plastic bottles, aluminum cans, and the like. A particularly cost-effective manner of labeling beverage containers utilizes a continuous web of pre-printed polymer label material that is cut into predetermined lengths, supplied with adhesive, and applied directly to the surface of a container. Adhesive costs may also be reduced by applying adhesive only to the leading and trailing edges of individual labels and wrapping the labels completely around the containers.
Label machines have been developed that are capable of relatively high-speed operation, e.g., as high as 750 containers/minute or more. However, such machines have been found to be limited in several respects.
One significant problem associated with such conventional labeling machines is that it is difficult to reliably control tension in a web of label material being processed at high speed. Among other concerns, a large roll of label material spun at high speed has a great deal of momentum, which often necessitates a dedicated tensioning mechanism between a supply of label material and a cutting mechanism. A tensioning mechanism, however, can introduce variable tensions at different points along the web, not to mention adding complexity and increasing the cost of the machines. Moreover, in many conventional label machine designs, separate cutting and transfer (or vacuum) drums are utilized, with the web at least partially drawn to a downstream transfer drum prior to severing a label from the web with an upstream cutting drum--an arrangement that can introduce variable tension to the web before and after cutting.
As a result of these tensioning concerns, most conventional labeling machines require that a non-stretchable polymer film such as polypropylene or polystyrene be used as the web material. Stretchable polymer films such as polyethylene are often unsuitable for use with such machines because the varied tensions in the web can stretch such films lengthwise and introduce unacceptable positioning errors when cutting the web. Web material constructed from non-stretchable polypropylene or polystyrene, however, can be three or four times more expensive than a stretchable material such as polyethylene. As a result, many conventional labeling machines prohibit the ability of a producer to take advantage of the substantial savings that could otherwise be realized through the use of less expensive films.
Therefore, a significant need exists in the art for an improved manner controlling tension in a web of material, particularly when supplying a web of label material in high speed labeling machines and the like. Moreover, a significant need exists for a manner of controlling web tension such that less expensive stretchable polymer films may be utilized in high speed labeling applications.
The process of conveying articles such as containers past a label transport drum introduces another significant problem associated with conventional labeling machines, as well as with other machinery that utilizes multiple stations that require different transport parameters at different stations. For example, with regard to labeling machines, many conventional labeling machine designs utilize turrets or star wheels to convey individual articles past a label transfer drum at a controlled rate and with a controlled separation, or "pitch", between sequential articles so that each article is initially presented to the transfer drum at a position thereon where a leading edge of a label is located. A turret is typically a rotatable body that includes mechanisms disposed about the periphery for gripping articles from the top and bottom ends thereof. A star wheel is typically a rotatable body that includes pockets disposed around its periphery that contact the sides of articles to advance the articles through the machine. Articles moving past a transfer drum are typically rotated as they pass the transfer drum (e.g., by virtue of contact between the drum and a fixed guide) so that labels on the drum are wrapped around the articles.
Turrets typically provide the greatest degree of precision in handling and transporting articles. However, due to the additional components and coordinated movements required to bring top and/or bottom gripping mechanisms into contact with articles, turrets are relatively slow and expensive. Star wheels are typically faster and less expensive, but have the drawback that articles are not held as securely and can become misaligned within the star wheels.
For example, star wheels are typically used in conjunction with a moving conveyor that supports the articles and moves at a fixed linear velocity. A label transfer drum then rotates with its outer surface traveling in the same direction as the conveyor. The velocities of the pockets in the star wheel and the outer surface of the drum are typically matched so that an article contacts a label on the drum while each is traveling at the same velocity. The articles may also be rolled or spun about its longitudinal axis to wrap the label around the article--typically by passing the article by a fixed guide or contacting the article with a relatively faster-moving belt.
Given that the leading edges of successive labels are spaced apart from one another along the outer surface of the transfer drum, it is often necessary for articles to be spaced apart with the proper pitch to ensure proper alignment of articles and labels. This typically requires that the star wheel and transfer drum rotate in such a manner that the articles and labels travel faster than the conveyor. However, unless the linear velocities of the articles are identical to that of the conveyor, the articles may become tilted within the pockets of the star wheel due to friction as the articles slide along the surface of the conveyor. As a result, applied labels may have loose or bunched-up portions due to the misalignment of the articles relative to the labels.
Moreover, other than when the labels are actually applied, it is often desirable to minimize the rotation of articles while disposed upon the conveyors so that the articles are conveyed in a more controlled manner. Conventional star wheels, which operate at a constant velocity, are often not capable of adequately controlling the rate of rotation of articles, which can result in label mis-registration and/or article jams at high speed.
Some conventional designs also incorporate feed screws at the entry and/or discharge ends of a label application station to convey the articles in a linear direction. The feed screws may also have variable pitches to control the linear velocity of the articles, and thus the separation between articles. However, feed screws also are unable to accurately control the rotational rates of articles, and thus, label mis-registration and/or article jams still remain a significant concern.
Therefore, a significant need also exists for an improved manner of conveying articles such as containers past a transfer drum in high speed applications, in particular so that the movement of such articles are carefully controlled.